The present invention relates to carbon foam materials derived from coal and more particularly to such foams that exhibit lower densities but equal strengths than similar prior art such materials.
U.S. patent applications Ser. No. 09/453,729 filed Dec. 12, 1999 and Ser. No. 09/902,828 filed on Jul. 10, 2001 both describe porous coal-based materials having a density of between about 0.1 g/cm3 and about 0.6 g/cm3 that are produced by the controlled heating of small coal particulate in a xe2x80x9cmoldxe2x80x9d and under a non-oxidizing atmosphere. The coal starting material preferably exhibits a free swell index of between about 3.5 and about 5.0 and most preferably between about 3.75 and about 4.5. The porous product thereby produced can be machined, adhered and otherwise fabricated to produce a wide variety of low cost, low density products, or used in its preformed shape as a filter, heat or electrical insulator etc. Such porous products, without further treatment exhibit compressive strengths of up to about 6000 psi. Further treatment by carbonization or graphitization yields products that can be used as electrical or heat conductors. Methods for the production of these coal based cellular products are also described in these applications.
While the coal based foam products produced in accordance with the methods described in these applications provide significant strength relative to their densities and are relatively easy to produce and fabricate, foams of even lower density, but of comparable strength that are somewhat more flexible in their manufacturing processes would be highly desirable. For example, the ability to produce very complicated shapes without first having to produce an oversized monolith and then xe2x80x9cmachiningxe2x80x9d the shape therefrom would be highly desirable.
The availability of a plastic, xe2x80x9cpre-blendedxe2x80x9d composition ready for processing into foam of a lower density than previously available from coal would also be advantageous.
It is therefore an object of the present invention to provide a method for the production of coal-based carbon foams of lower density than but equal strength as those previously available in the prior art.
Is another object of the present invention to provide a method for the manufacture of coal-based carbon foams that lends itself to the production of such materials from highly plastic precursor blends that simplify the formation and production of coal-based foam products, especially those possessing highly complex shapes.
According to the present invention, there is provided a method for the manufacture of coal-based carbon foams from a coal particulate starting material that comprises blending from 1 to about 10% by weight of pitch with the coal particulate before foaming. Blends of coal-based particulate with 1 to about 10% by weight of pitch as well as coal-based carbon foams manufactured from such blends are also described.